Get an iPod Classic. Apple is very unlikely to update it (what could they do anyways?) and if at all, they would probably update the iPod touch or iPod Nano.
This might be a long shot, but I know that as recently as a few years ago Apple still stocked many of the older classic iPods as service replacements for customers who still had those older iPods. Obviously the price to replace the units outside of warranty was and would be roughly the same as buying a new iPod classic it's worth a call to AppleCare or a short trip to your local Apple stores Genius Bar.